Bacterial expression and functional characterization of a rat thyroid hormone sulfotransferase, ST1B1

At least three forms of phenol sulfotransferase (ST) ST1B1, ST1A1 and ST1C1 are contained in rat livers. To identify the form contributing to the meta bolism of 3,3:5-triiodothyronine (T-3), functional characterization of thes e forms was performed by expression in Escherichia coli. ST1B1 and ST1C1 we re shown to be active on sulfation towards T-3 With high affinity (K-m: 44. 4 and 25.8 mu M, respectively), whereas ST1A1 had low affinity. In Western blotting using antibodies raised against the individual ST, hepatic content s of each ST were quantitatively determined. ST1B1 showed no dear sex-diffe rence, whereas the level of ST1C1 was higher in adult males than adult fema les. The content of ST1B1 was 1.4, 6.8 and 10 times higher than that of ST1 C1 in adult males, adult females and both sexes of immature rats, respectiv ely. The developmental pattern of ST1B1 was similar to that of ST1A1, but d iffered from that of ST1C1. These results indicate that ST1B1 and ST1C1 are involved in T-3 metabolism in rats and ST1B1 is the constitutive form acro ss sexes and ages.